The invention relates to a method for producing crema in a coffee vending machine which comprises a flow-through heater for heating water and which can be charged with substrate capsules comprising a Venturi nozzle for crema production, said method comprising the following continuously executed steps:
heating the water in the flow-through heater
brewing the ground coffee using the heated water in a brewing chamber in order to produce a coffee drink and
producing crema by mixing the coffee drink with a gas in the Venturi nozzle.
The invention furthermore relates to a corresponding device for carrying out this method.
Coffee drinks, espressos in particular, have a light fine foam, the so-called crema, formed on their surface as a result of the high pressure of between 2 and 10 bar under which they are produced. If coffee drinks are produced under lower pressure however, typically at approximately 1 bar, the pressure based physicochemical processes involved in espresso production do not occur. Although a foam can form, as a rule this has neither a fine bubble structure nor a lasting character however. In order nevertheless to obtain a crema having a fine bubble structure, the coffee drink can among other things be directed through a Venturi nozzle. In said Venturi nozzle the bubble size of the foam can be set relatively exactly and as homogeneous a size distribution of the foam bubbles as possible can be achieved. The crema thus produced is furthermore also very stable, or firm. The relevant parameters for the crema production in a Venturi nozzle are on the one hand the flow rate of the coffee drink through the nozzle and on the other hand the cross-section of the hole through which a gas, ambient air as a rule, is drawn in in order to form the foam. Both the flow rate and also the hole diameter determine the quantity of gas blown in.
A multiple-drink vending machine is on the market which can be charged with drink substrate capsules and with which coffee can also be produced in addition to tea, drinking chocolate and even soups. Since as a rule no foam production is desired for the other drinks, the Venturi nozzle required for the crema production is arranged not at the machine end but in the capsule. In order to improve the crema formation at the machine end it is not therefore possible to fall back on the dimensioning of the Venturi nozzle.